Constant voltage ring and constant current ring automatic switching circuit and linear power supply

Abstract

The invention discloses a constant voltage ring and constant current ring automatic switching circuit and a linear power supply, and belongs to the technical field of electrical variable adjustment. Wherein the constant voltage ring comprises a differential sampling link, a direct current bias link and an integration link; the constant current loop comprises a proportional element and an integral element. A differential sampling circuit is arranged in the constant-voltage ring to sample the output voltage of the power supply, the differential sampling circuit is matched with a direct-current bias link to provide superposed voltage for an integration link in the constant-voltage ring, the superposed voltage is compared with set voltage, the switching-in time of the constant-voltage ring is determined, and therefore the constant-current ring can be switched to the constant-voltage ring in advance, and the switching-in time of the constant-voltage ring is determined. And the problem of overshoot of the output voltage of the power supply is prevented. According to the linear power supply, in the process of switching from the constant current stage to the constant voltage stage, the output voltage can be smoothly transited to the target voltage, the condition of step-shaped rising cannot occur, and the switching process is natural and rapid.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric variable regulation, and relates to a linear power supply, in particular to an automatic switching circuit of a constant voltage loop and a constant current loop for stabilizing the output voltage or output current of the linear power supply. Background Art

[0002] When using an external power supply to test the performance of a battery cell, it is necessary to control the voltage and current output by the external power supply, such as Figure 2 As shown, the battery cell can first enter the constant current charging stage, and then enter the constant voltage charging stage after the battery voltage rises to the target voltage. After the constant voltage test is completed, the battery cell is controlled to enter the discharge stage to detect whether the battery voltage will suddenly drop and then rise again.

[0003] In view of the above-mentioned testing requirements of the battery cells, the external power supply is required to be able to cooperate with the battery cells to output a voltage with high linearity, so that the performance testing of the battery cells can be better achieved.

[0004] During the constant-current charging phase, the output current of the external power supply must remain stable, so a constant-current loop is required to detect and regulate the output current. During the constant-voltage charging phase, the output voltage of the external power supply must remain stable, so a constant-voltage loop is required to detect and regulate the output voltage. Furthermore, the constant-current and constant-voltage loops must be able to automatically switch between them, allowing the battery cell charging process to automatically transition from the constant-current phase to the constant-voltage phase and avoid output voltage overshoot.

[0005] In order to meet the above design requirements, the Chinese invention patent application with publication number CN118523613A discloses a constant voltage control circuit, a constant voltage constant current control circuit and a source meter, such as Figure 1 As shown, the constant current control loop uses an operational amplifier AMP0, the feedback current I_fb Transmitted to the inverting terminal of the operational amplifier AMP0 through the resistor R10, setting the current I_set The feedback voltage is transmitted to the non-inverting terminal of the op amp AMP0 through the resistor R11. The constant voltage control loop uses two op amps AMP1 and AMP2. The control loop where the op amp AMP1 is located is the main constant voltage control loop, and the control loop where the op amp AMP2 is located is the auxiliary constant voltage control loop. V_fb The voltage is transmitted to the inverting terminal of the op amp AMP1 through the resistor R2, and is transmitted to the inverting terminal and the non-inverting terminal of the op amp AMP2 through the resistors R5 and R7 respectively. V_set The voltage is transmitted to the non-inverting terminal of the operational amplifier AMP1 and the non-inverting terminal of the operational amplifier AMP2 through the resistors R3 and R6 respectively.

[0006] The working principle of the above control loop is: when the constant current loop works, the output voltage is determined by the load voltage and is lower than the set voltage V_set At this time, the main constant pressure ring satisfies the relationship V_fb <V_set=V_ref1 , in saturation state. For the auxiliary constant voltage loop, compared with the main constant voltage loop, due to the addition of resistor R7, without considering the resistor R8, we can get: V_ref2= [ R6 / ( R6+ R7 )]×( V_set-V_fb ) +V_fb From this formula, we can see that the reference voltage V_ref2 Follow feedback voltage V_fb changes with the change of the reference voltage V_ref2 Automatic adjustment function, and meet V_fb <V_ref2<V_set As the output voltage continues to rise, the feedback voltage V_fb The reference voltage also increases accordingly. V_ref2 With the feedback voltage V_fb However, due to the effect of capacitor C6, the reference voltage V_ref2 The rise rate is slower than the feedback voltage V_fb The rising speed will satisfy V_ref2 <V_fb<V_set At this time, although the output voltage has not reached the set voltage V_set , but the auxiliary constant voltage loop can exit saturation and enter the working state, which makes the constant current loop exit work early. At this time, the main constant voltage loop is still in saturation, and the output voltage is controlled by the auxiliary constant voltage loop, and the voltage regulation value is V_ref2 <V_set In order to make the auxiliary constant voltage loop stop working, it is necessary to add power supply Vcc and resistor R8 to the non-inverting terminal of op amp AMP2. Ignoring the influence of resistor R7, we can get: V_ ref2= [ R6 / ( R6+R8 )]×( V_cc-V_set ) +V_set>V_set=V_ref1 At this time, the output of op amp AMP2 is saturated and stops working, and the output voltage is controlled by the main constant voltage loop.

[0007] By adding an auxiliary constant voltage loop, the control loop can shorten the loop response time and reduce the probability of output voltage overshoot when switching from the constant current stage to the constant voltage stage. However, there are the following problems: 1) An additional set of auxiliary constant-voltage loops is required, and a Vcc power supply is required to control the switching between the main and auxiliary constant-voltage loops. Since the timing of Vcc introduction is difficult to accurately control, the switching response time between the main and auxiliary constant-voltage loops is uncertain.

[0008] 2) It can only ensure that the output voltage does not overshoot, but cannot make the output voltage reach a stable state smoothly. Specifically, the process of switching from the auxiliary constant voltage loop to the main constant voltage loop must take some time, during which time the output voltage will remain at the regulated value. V_ref2 ( <V_set ) does not change until the main constant voltage loop is turned on, the output voltage will continue to rise and eventually reach the set voltage V_set This results in a step-like rise in the output voltage, such as Figure 2 The part circled in the middle cannot achieve a smooth transition of the output voltage.

[0009] 3) In the constant current stage, it is impossible to achieve low current ( <1mA ) stable output. Because in actual application, there will be a dummy load with a certain resistance on the output side of the power module. The dummy load will absorb part of the current, making it impossible for the load to be charged to the set voltage. Summary of the Invention

[0010] The purpose of the present invention is to provide an automatic switching circuit between a constant voltage loop and a constant current loop, which can realize the early natural switching from the constant current loop to the constant voltage loop, while preventing the output voltage from overshooting and ensuring a smooth transition of the output voltage during the switching process.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solutions: In one aspect, the present invention provides a circuit for automatically switching between a constant voltage loop and a constant current loop, for controlling a power supply to first charge a load with a constant current and then with a constant voltage; a voltage reference point and a negative voltage sampling point are configured on the output side of the power supply, a capacitor is connected in series between the voltage reference point and the negative voltage sampling point, and the voltage reference point is used as a reference ground for the constant voltage loop and the constant current loop; The constant pressure ring is equipped with: The differential sampling link includes a first operational amplifier, wherein the inverting input terminal of the first operational amplifier is connected to the negative voltage sampling point through a parallel branch of an input resistor and an input capacitor, the non-inverting input terminal is connected to the reference ground, and the output terminal is reversely connected to the inverting input terminal of the first operational amplifier through a parallel branch of a differential resistor and a differential capacitor; the first operational amplifier outputs the feedback value of the output voltage of the power supply V fb ,and ;in, ,and R201 is the resistance value of the input resistor, R202 is the resistance of the differential resistor, VOUT- is the voltage value at the negative voltage sampling point; k is the proportional coefficient of the differential sampling link, is the rate of change of the output voltage of the power supply; A DC bias link includes an instrument amplifier, the non-inverting input of the instrument amplifier receives the feedback value V fb , the inverting input terminal is connected to the reference ground, and the output superimposed voltage V fb + VREF ;in, VREF is the DC bias voltage of the instrumentation amplifier; The integration link is composed of an integration circuit formed by a third operational amplifier and a peripheral circuit. The inverting input terminal of the third operational amplifier receives the superimposed voltage output by the instrumentation amplifier, and the non-inverting input terminal receives the set voltage. V set , the output end is connected to the cathode of the first diode, the anode of the first diode is connected to the pull-up circuit, and an analog switch control signal is generated to control the conduction degree of the switch tube configured on the output side of the power supply; The constant current loop is configured with: The proportional link is composed of an operational amplifier and a peripheral circuit to form a proportional circuit. The inverting input terminal of the operational amplifier receives the sampled current value at the voltage reference point, the non-inverting input terminal is connected to the reference ground, and the output current value after proportional adjustment is obtained. I m ; The integration link is composed of a seventh operational amplifier and a peripheral circuit to form an integration circuit, and the inverting input terminal of the seventh operational amplifier receives the current value I m , the non-inverting input terminal receives the set current value I set The output end is connected to the cathode of the second diode, and the anode of the second diode is connected to the pull-up circuit, which is used to adjust the potential of the switch control signal.

[0012] In some embodiments of the present application, in order to solve the problem that the power supply cannot achieve a small current ( I set <1mA ) To solve the problem of stable output, the present application further configures a current compensation link in the constant current loop, which includes a fourth operational amplifier, the non-inverting input terminal of the fourth operational amplifier is connected to the negative voltage sampling point, the inverting input terminal is connected to the output terminal of the fourth operational amplifier, and the output terminal of the fourth operational amplifier is connected to the inverting input terminal of the seventh operational amplifier. By reducing the current of the inverting input terminal of the seventh operational amplifier, the constant current loop is operated. I m Can gradually rise and exceed I set By appropriately increasing the output current of the power supply, the current absorbed by the dummy load on the output side of the power supply is compensated, so that the load can be charged to the target voltage.

[0013] In some embodiments of the present application, the output terminal of the fourth operational amplifier can be connected to the inverting input terminal of the seventh operational amplifier through a first compensation resistor connected in series with the fourth operational amplifier, and the current value output by the proportional link is I m The current is transmitted to the inverting input terminal of the seventh operational amplifier through the second compensation resistor; when the target current is less than 1 mA In the constant current working mode, the ratio of the first compensation resistor to the second compensation resistor is reasonably adjusted according to the current absorbed by the dummy load, so as to accurately compensate for the missing current.

[0014] In some embodiments of the present application, in order to >1mA ) Constant current charging stage, to reduce the influence of the current compensation link on the output current of the power supply, a resistor voltage divider network can be configured in the current compensation link, and the resistor voltage divider network is connected between the negative voltage sampling point and the reference ground, and its voltage dividing node is connected to the non-inverting input terminal of the fourth operational amplifier. At the same time, the non-inverting input terminal of the fourth operational amplifier is connected to the reference ground through a filter capacitor. By adjusting the voltage divider ratio, the current output by the current compensation link can significantly affect the current value during the low current constant current charging stage. I m In the high current constant current charging stage, the current output by the current compensation link has a significant impact on the current value. I m The impact produced can be ignored, so that the constant current loop of the present application can meet the constant current charging requirements of different loads.

[0015] In some embodiments of the present application, two-stage operational amplifiers can be set in the proportional link, namely the fifth operational amplifier and the sixth operational amplifier; the inverting input terminal of the fifth operational amplifier is configured to receive the sampled current value at the voltage reference point, the non-inverting input terminal is connected to the reference ground, and the output terminal is connected to its own inverting input terminal and the inverting input terminal of the sixth operational amplifier respectively, the non-inverting input terminal of the sixth operational amplifier is connected to the reference ground, the output terminal is connected to its own inverting input terminal, and the current value after the proportional adjustment is output. I m , connected to the inverting input terminal of the seventh operational amplifier through the second compensation resistor. The sampling current value and the set current value of this application I set It is expressed in voltage. For the sampling current value, a sampling resistor can be connected in series at the voltage reference point, and the voltage across the sampling resistor is used as the sampling current value at the voltage reference point, which is transmitted to the constant current loop to perform constant current control on the power supply.

[0016] This application configures a fifth op amp to amplify or reduce the voltage value corresponding to the sampled current by a certain ratio and invert it to a negative voltage value. The sixth op amp inverts the negative voltage value again to a positive voltage value for comparison with the set current value. Compared to a proportional circuit designed with a single op amp, the two-stage op amp design provides more flexible adjustment of the voltage value corresponding to the sampled current. For sampled currents with a wide range of variation, the corresponding voltage value can be kept within an appropriate range for comparison with the set current value.

[0017] In another aspect, the present invention further provides a linear power supply, comprising: A rectifier circuit, which is used to rectify the input AC power into a DC power; a current limiting and voltage stabilizing circuit, which is used to perform current limiting and voltage stabilization processing on the DC power output by the rectifier circuit, and output a stable DC bus voltage; A switch tube module is used to connect or disconnect the line between the DC bus voltage and the output side of the power supply; a voltage reference point and a negative voltage sampling point are configured on the output side of the power supply, a capacitor is connected in series between the voltage reference point and the negative voltage sampling point, and the voltage reference point is used as the reference ground for the constant voltage loop and the constant current loop; The constant pressure ring comprises: The differential sampling link includes a first operational amplifier, wherein the inverting input terminal of the first operational amplifier is connected to the negative voltage sampling point through a parallel branch of an input resistor and an input capacitor, the non-inverting input terminal is connected to the reference ground, and the output terminal is reversely connected to the inverting input terminal of the first operational amplifier through a parallel branch of a differential resistor and a differential capacitor; the first operational amplifier outputs the feedback value of the output voltage of the power supply V fb ,and ;in, and R201 is the resistance value of the input resistor, R202 is the resistance of the differential resistor, VOUT- is the voltage value at the negative voltage sampling point; k is the proportional coefficient of the differential sampling link, is the rate of change of the output voltage of the power supply; A DC bias link includes an instrument amplifier, the non-inverting input of the instrument amplifier receives the feedback value V fb , the inverting input terminal is connected to the reference ground, and the output superimposed voltage V fb + VREF ;in, VREF is the DC bias voltage of the instrumentation amplifier; The integration link is composed of an integration circuit formed by a third operational amplifier and a peripheral circuit. The inverting input terminal of the third operational amplifier receives the superimposed voltage output by the instrumentation amplifier, and the non-inverting input terminal receives the set voltage. V set , the output end is connected to the cathode of the first diode, the anode of the first diode is connected to the pull-up circuit, and an analog switch control signal is generated; The constant current loop is configured with: The proportional link is composed of an operational amplifier and a peripheral circuit to form a proportional circuit. The inverting input terminal of the operational amplifier receives the sampled current value at the voltage reference point, the non-inverting input terminal is connected to the reference ground, and the output current value after proportional adjustment is obtained. I m ; The integration link is composed of a seventh operational amplifier and a peripheral circuit to form an integration circuit, and the inverting input terminal of the seventh operational amplifier receives the current value I m , the non-inverting input terminal receives the set current value I set The output end is connected to the cathode of the second diode, and the anode of the second diode is connected to the pull-up circuit, which is used to adjust the potential of the switch control signal; the switch control signal controls the conduction degree of the switch tube module, so that the linear power supply first charges the subsequent load with constant current and then with constant voltage.

[0018] In some embodiments of the present application, in order to increase the output power of the linear power supply, two parallel MOS tubes can be configured in the switching tube module, and the gate-source voltages of the two MOS tubes can be adjusted using the switching control signal to adjust the conduction degree of the two MOS tubes.

[0019] In some embodiments of the present application, the rectifier circuit can be configured as a 7-fold voltage rectifier circuit constructed by diodes and capacitors to obtain a sufficiently high DC bus voltage.

[0020] In some embodiments of the present application, the current limiting and voltage stabilizing circuit may be configured to include: A first MOS transistor, whose drain is connected to the DC output side of the rectifier circuit through an anti-reverse bias diode, and whose source is connected to its gate through a second current-limiting resistor to prevent excessive current in the loop; a second MOS transistor, wherein the drain is connected to the gate of the first MOS transistor, the source of the second MOS transistor is connected to the gate of the second MOS transistor via a third current-limiting resistor, and is connected to the DC bus voltage output terminal via a charging current-limiting resistor; the combination of the first MOS transistor and the second current-limiting resistor serves as a current limiting path for the second MOS transistor, thereby preventing excessive current from flowing through the second MOS transistor; a third MOS transistor, wherein the drain of the third MOS transistor is connected to the gate of the second MOS transistor, and the source of the third MOS transistor is connected to the gate of the third MOS transistor via a fourth current-limiting resistor; the combination of the second MOS transistor and the third current-limiting resistor serves as a current limiting path for the third MOS transistor, thereby preventing excessive current from flowing through the third MOS transistor; a resistor voltage divider circuit, connected between the source of the second MOS transistor and ground, with a voltage divider node connected to the gate of the third MOS transistor; The cathode of the voltage regulator tube is connected to the source of the third MOS tube, and the anode is grounded, so as to stabilize the DC bus voltage. The combination of the third MOS tube and the fourth current-limiting resistor provides a current limiting path for the voltage regulator tube to prevent excessive current flowing through the voltage regulator tube.

[0021] In some embodiments of the present application, in order to meet the test requirements of the load in the voltage self-holding stage, a load voltage self-holding circuit can be set in the linear power supply, which includes a switching tube connected between the voltage reference point and the load and a holding resistor connected at both ends of the load. The switching tube is disconnected when the load requires voltage self-holding, so that the load and the holding resistor form a loop and enter the voltage self-holding stage.

[0022] In some embodiments of the present application, in order to meet the test requirements of the load during the discharge phase, a discharge circuit may be further provided in the linear power supply, which includes a switching element connected to the positive electrode of the load and a discharge resistor connected to ground. The switching element is turned on when the linear power supply stops outputting voltage and the load needs to be discharged, and the charge in the load is released through the discharge resistor.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are mainly reflected in: 1. The present invention samples the output voltage of the power supply by setting a differential sampling circuit in the constant voltage loop, and cooperates with the DC bias link to provide a superimposed voltage for the integral link in the constant voltage loop. The superimposed voltage is compared with the set voltage to determine the cut-in time of the constant voltage loop, thereby enabling the constant current loop to switch to the constant voltage loop in advance to prevent the problem of power supply output voltage overshoot.

[0024] 2. The present invention does not need to set two voltage setting values for the constant voltage ring, nor does it need to add a power supply that needs to control the introduction time. The entire switching process can be completed automatically according to the actual output voltage and current of the power supply. There is no need to design control logic. The solution is simple to implement and the pure hardware circuit design has high reliability.

[0025] 3. When the linear power supply of the present invention switches from the constant current stage to the constant voltage stage, its output voltage can smoothly transition to the target voltage without a step-like increase, and the switching process is natural and fast.

[0026] 4. The present invention can realize a small constant current output of the linear power supply by setting a current compensation link in the constant current loop, thereby solving the problem that the load cannot be charged to the target voltage because the output current of the power supply is too small and is absorbed by the dummy load on the output side of the power supply.

[0027] Other features and advantages of the present invention will become more apparent after reading the detailed description of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a circuit schematic diagram of an embodiment of an existing constant voltage and constant current control circuit; Figure 2 is based on Figure 1 The output voltage curve diagram of the power supply designed with constant voltage and constant current control circuit in the constant current stage, constant voltage stage and discharge stage shown in the figure; Figure 3 This is a circuit principle block diagram of an embodiment of the linear power supply proposed by the present invention; Figure 4 yes Figure 3 A circuit schematic diagram of an embodiment corresponding to the circuit schematic block diagram shown; Figure 5 This is a circuit schematic diagram of an embodiment of the automatic switching circuit of the constant voltage loop and the constant current loop proposed by the present invention; Figure 6 It is an output voltage curve diagram of the linear power supply proposed by the present invention in the constant current stage, constant voltage stage and discharge stage. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0031] See also Figure 3 The linear power supply of this embodiment primarily includes components such as a rectifier circuit, a current-limiting and voltage-stabilizing circuit, a switching module, a constant-voltage loop, and a constant-current loop. To accommodate multiple DC bus voltages, a bus switching circuit can be incorporated into the linear power supply to output DC bus voltages of varying amplitudes.

[0032] The rectifier circuit is used to rectify the external AC power supply into a DC power supply, and after being processed by the current limiting and voltage stabilizing circuit, a stable DC bus voltage is generated.

[0033] In some embodiments, the rectifier circuit can be designed as a voltage doubler rectifier circuit to increase the amplitude of the DC voltage while achieving AC-DC conversion. Figure 4 As shown, a 7-fold voltage rectifier circuit can be formed by using capacitors C101-C113 in combination with diodes D101-D107. The AC side is connected to the AC mains 220VAC through the first current limiting resistor R101. The DC side outputs the rectified and boosted DC power supply VCC (which can reach more than 1000V) and transmits it to the current limiting and voltage stabilizing circuit through the anti-reverse bias diode D108.

[0034] In this embodiment, a voltage regulator tube Z1 and multiple current limiting paths are configured in the current limiting and voltage stabilizing circuit. Figure 4 The figure shows three current-limiting paths formed by three N-channel MOS transistors and three current-limiting resistors. The first MOS transistor Q1 and the second current-limiting resistor R102 form the current-limiting path for the second MOS transistor Q2, which limits the current flowing through the second MOS transistor Q2. The second MOS transistor Q2 and the third current-limiting resistor R103 form the current-limiting path for the third MOS transistor Q3, which prevents excessive current flowing through the third MOS transistor Q3. The third MOS transistor Q3 and the fourth current-limiting resistor R104 form the current-limiting path for the voltage-stabilizing transistor Z1, which limits the current flowing through the voltage-stabilizing transistor Z1. In each current-limiting path, the current-limiting resistor is connected between the source and gate of the MOS transistor. The drain of the first MOS transistor Q1 is connected to the cathode of the reverse bias prevention diode D108, the anode of which is connected to the DC side of the rectifier circuit. The drain of the second MOS transistor Q2 is connected to the gate of the first MOS transistor Q1, and the source of the second MOS transistor Q2 is connected to the DC bus voltage output terminal VBUS1 through the charging current-limiting resistor R110. The drain of the third MOS transistor Q3 is connected to the gate of the second MOS transistor Q2, and the source of the third MOS transistor Q3 is connected to the voltage regulator Z1. Voltage-dividing resistors R106-R109 are connected between the source of the second MOS transistor Q2 and the gate of the third MOS transistor Q3, and a voltage-dividing resistor R105 is connected between the gate of the third MOS transistor Q3 and ground. Resistors R105-R109 form a resistor divider network to divide the DC voltage VCC output by the rectifier circuit.

[0035] Specifically, when the voltage generated by the resistor divider circuit at both ends of the voltage divider resistor R105 exceeds the reverse breakdown voltage of the voltage regulator tube Z1 V Z1 When the voltage regulator Z1 comes into play, the voltage across its two ends is limited to V Z1Since the current flowing through the third MOS transistor Q3 has been limited by the current limiting path formed by the second MOS transistor Q2 and the third current limiting resistor R103, the voltage across the fourth current limiting resistor R104 will reach a fixed value, which is recorded as V R104 At this time, the voltage across the voltage divider resistor R105 is V Z1 + V R104 , then the voltage of the DC bus voltage output terminal VBUS1 is ( V Z1 + V R104 ) × (R105 + R106 + R107 + R108 + R109) / R105. Therefore, by properly configuring the resistance of the voltage divider resistors R105-R109 and adjusting the voltage divider ratio of the resistor divider circuit, the voltage amplitude at the DC bus voltage output terminal VBUS1 can be set. The DC bus voltage here is also represented by VBUS1.

[0036] By dividing the DC bus voltage VBUS1 through a voltage divider network consisting of resistors R111-R114 and capacitors C114-C117, a DC bus voltage VBUS2 of a different amplitude can be output. In some embodiments, the DC bus voltage VBUS2 after voltage division can be configured to be half of the DC bus voltage VBUS1 before voltage division to meet different charging voltage requirements of the load.

[0037] In order to realize the switching output of DC bus voltages of different amplitudes, a MOS tube Q4 and a diode D109 can be set in the bus switching circuit, such as Figure 4 shown.

[0038] The drain and source of the MOS transistor Q4 can be connected between the DC bus voltage VBUS1 before voltage division and the bus voltage output point VBUS. The gate receives the bus switching signal (control 1). When the load requires a charging voltage with a higher amplitude, the MOS transistor Q4 is controlled to be turned on and output the DC bus voltage VBUS1 before voltage division.

[0039] In some embodiments, a current limiting resistor R115 may be connected between the gate and source of the MOS transistor Q4 to prevent excessive current in the loop.

[0040] Diode D109 is connected between the divided DC bus voltage VBUS2 and the bus voltage output point VBUS. When MOS transistor Q4 is turned on, the high-amplitude DC bus voltage VBUS1 reverse-biases diode D109, cutting off the output path of DC bus voltage VBUS2. When MOS transistor Q4 is turned off, the divided DC bus voltage VBUS2 controls diode D109 to conduct, allowing the divided DC bus voltage VBUS2 to charge the load.

[0041] The selected output DC bus voltage (also represented by VBUS) is transmitted to the output side of the linear power supply through the switching tube module. The switching tube module is controlled by the constant current loop and constant voltage loop to turn it on or off to control the linear power supply to operate in the constant current stage or constant voltage stage.

[0042] In order to adjust the output voltage and output current of the linear power supply, such as Figure 4 As shown, in this embodiment, a voltage reference point OUT is first set at the output side of the linear power supply. The voltage at the voltage reference point OUT is the output voltage of the linear power supply. Vout The output voltage of this embodiment is Vout The amplitude range is between 0V and 1300V. The voltage reference point OUT is connected to the negative voltage sampling point VOUT- through the capacitor C118 to generate a sampling voltage in the voltage range of -1300V to 0V as the input of the constant voltage loop and the constant current loop. The current at the voltage reference point OUT is collected as the input of the constant current loop. In this embodiment, a sampling resistor R120 can be connected in series between the voltage reference point OUT and the switching tube module to convert the sampling current into a voltage value across the sampling resistor R120 (hereinafter represented by the sampling current value Isense) as the input of the constant current loop. At the same time, the voltage reference point OUT is used as the reference ground for the constant voltage loop and the constant current loop.

[0043] Secondly, based on the test requirement that the load (such as battery cells) is first charged with constant current and then with constant voltage, a constant current loop circuit and a constant voltage loop circuit are designed to control the linear power supply to operate in the constant current stage first and then automatically switch to the constant voltage stage, while ensuring that the output voltage does not overshoot.

[0044] like Figure 5 As shown, in this embodiment, the constant voltage loop and the constant current loop are designed to be in parallel structure, and cooperate with the pull-up circuit to generate an analog switch control signal V / I to control the conduction degree of the switch tube module.

[0045] In some embodiments, the constant voltage loop may be composed of main parts such as a differential sampling part, a DC bias part and an integral part.

[0046] Among them, the differential sampling link uses the first operational amplifier U1 (operational amplifier) to cooperate with the peripheral circuit to form a differential circuit, collecting the voltage at the negative voltage sampling point VOUT- to generate the feedback value of the output voltage of the linear power supply V fb .

[0047] Specifically, a parallel branch of an input resistor R201 and an input capacitor C201 is connected between the inverting input terminal of the first operational amplifier U1 and the negative voltage sampling point VOUT-, the non-inverting input terminal of the first operational amplifier U1 is connected to the reference ground through a resistor R203, and the output terminal of the first operational amplifier U1 is connected to the inverting input terminal of the first operational amplifier U1 through a parallel branch of a differential resistor R202 and a differential capacitor C202.

[0048] Since the gain expression of the differential sampling link of this embodiment is: ; in, s Represents the complex frequency. Therefore, from the gain expression, we can see that the constant voltage loop has a pole and a zero, and the angular frequency of the pole is , the angular frequency of the zero point , amplitude By configuring the input resistor R201 With input capacitance C201 The parameters can be used to adjust the advance of voltage feedback, and the advance is proportional to the rate of change of the output voltage.

[0049] Compared with the conventional method of using resistor voltage division to perform voltage sampling, the differential sampling method used in this embodiment can make the feedback value V fb It has a DC bias proportional to the output voltage rise rate, that is, ;in, k is the proportional coefficient set for the differential sampling link, and k=G 0 × R201 × C201 ; is the rate of change of the output voltage of the linear power supply.

[0050] The feedback voltage output by the first op amp U1 V fb The DC bias link is mainly composed of an instrumentation amplifier U2 and a resistor R204. The instrumentation amplifier U2 has a DC bias voltage. VREF Its non-inverting input terminal is connected to the output terminal of the first operational amplifier U1, and receives the feedback value output by the first operational amplifier U1. V fb ;in, , Here, use VOUT- It also represents the voltage value at the negative voltage sampling point. Connect the inverting input of the instrument amplifier U2 to the reference ground through resistor R204, and the voltage output by the instrument amplifier U2 is the superimposed voltage. , transmitted to the subsequent integration link.

[0051] In this embodiment, a third operational amplifier U3 is set in the integration link to form an integration circuit with the peripheral circuit, and the superimposed voltage output by the instrumentation amplifier U2 is compared with the set voltage. V set The comparison is performed to output a positive voltage (eg, 12V) or a negative voltage (eg, -12V) to control the first diode D201 to be turned on or off.

[0052] Specifically, the inverting input terminal of the third operational amplifier U3 is connected to the output terminal of the instrumentation amplifier U2 through the resistor R205, and the non-inverting input terminal of the third operational amplifier U3 receives the set voltage through the resistor R206. V set The output of the third op amp U3 is connected to the cathode of the first diode D201 via the integrating capacitor C203. The anode of the first diode D201 is connected to the inverting input of the third op amp U3 via the integrating capacitor C203. When the third op amp U3 outputs a positive voltage, the first diode D201 is turned off, and its anode potential VCON is high. Conversely, when the third op amp U3 outputs a negative voltage, the first diode D201 is turned on, and its anode potential VCON is pulled low.

[0053] Similarly, the constant current loop will also generate a high potential or low potential control signal ICON, and control the linear power supply to operate in constant current mode or constant voltage mode according to the control signal VCON generated by the constant voltage loop and the control signal ICON generated by the constant current loop.

[0054] In some embodiments, the constant current loop may be composed of main parts such as a proportional link, an integral link and a current compensation link.

[0055] Among them, the proportional link uses an op amp and peripheral circuits to form a proportional circuit, which proportionally adjusts the sampling current value Isense at the voltage reference point OUT and transmits it to the integral link and the set current I set The comparison is performed (expressed as a voltage value) to control the on / off of the second diode D202, thereby generating the control signal ICON.

[0056] In one embodiment, two-stage operational amplifiers U5 and U6 can be set in the proportional link, such as Figure 5As shown. Among them, the inverting input terminal of the fifth operational amplifier U5 is configured to receive the sampling current value Isense at the voltage reference point OUT through the resistor R210, the non-inverting input terminal is connected to the reference ground through the resistor R212, and the output terminal is connected to the inverting input terminal of the fifth operational amplifier U5 through the resistor R211. The sampling current value Isense can be amplified or reduced by a certain proportion through the fifth operational amplifier U5, and after being inverted to a negative voltage value, it is connected to the inverting input terminal of the sixth operational amplifier U6 through the resistor R213. The non-inverting input terminal of the sixth operational amplifier U6 is connected to the reference ground through the resistor R214, and the output terminal is connected to its own inverting input terminal through the resistor R215, so that the negative voltage value output by the fifth operational amplifier U5 is inverted to a positive voltage value again, and the current value is obtained. Im It is represented and transmitted to the integration link of the subsequent stage.

[0057] The integral link in the constant current loop can use the seventh operational amplifier U7 to cooperate with the peripheral circuit to form an integral circuit, and the inverting input terminal of the seventh operational amplifier U7 is connected to the output terminal of the sixth operational amplifier U6 through the second compensation resistor R216 to receive the current value output by the proportional link. I m , configure the non-inverting input of the seventh operational amplifier U7 to receive the set current through the resistor R217 I set (expressed as a voltage value) and connected to the reference ground via filter capacitor C206. The output of the seventh op amp U7 is connected to the cathode of the second diode D202, and the anode of the second diode D202 is connected to the inverting input of the seventh op amp U7 via integrating capacitor C207. When the seventh op amp U7 outputs a positive voltage, the second diode D202 is cut off, and its anode potential ICON is high. Conversely, when the seventh op amp U7 outputs a negative voltage, the second diode D202 is turned on, and its anode potential ICON is pulled down to a low level.

[0058] The pull-up circuit is designed to connect to the anodes of the first diode D201 and the second diode D202, respectively, to stabilize the potential of the control signals VCON and ICON at a high level, thereby generating a switch control signal V / I for controlling the switch module. The switch control signal V / I is an analog signal used to adjust the conduction level of the switch.

[0059] In some embodiments, the pull-up circuit may be formed by connecting a positive voltage 12VOUT (eg, 12V) and a pull-up resistor R224, as shown in FIG. Figure 5 The positive voltage 12VOUT is connected to the anodes of the first diode D201 and the second diode D202 through the pull-up resistor R207, and the connection node between the pull-up circuit and the first diode D201 and the second diode D202 is used as the output end of the switch control signal V / I.

[0060] The working principle of the constant pressure ring and constant current ring is: The output voltage of the linear power supply is determined by the load voltage. When the linear power supply starts to charge the load, the output voltage of the linear power supply is 0V.

[0061] When the output voltage of the linear power supply is 0V, the feedback voltage output by the differential sampling link in the constant voltage loop is V fb Since the instrumentation amplifier U2 has a DC bias voltage VREF, the voltage output by the instrumentation amplifier U2 is VREF, which is transmitted to the subsequent integration link. V set When not given, the integral link outputs a negative voltage (for example, -12V), causing the first diode D201 to be turned on, the constant voltage loop to be cut in, and to control the switch tube module in the linear power supply; at this time, the second diode D202 is cut off, the constant current loop is not cut in, and has no effect.

[0062] When setting voltage V set After the given voltage is set, the voltage at the non-inverting input of the third operational amplifier U3 in the constant voltage loop is the set voltage. V set , higher than the voltage at its inverting input, the third op amp U3 outputs a positive voltage (e.g., 12V), turning off the first diode D201. At this point, the positive voltage 12VOUT from the pull-up circuit, through pull-up resistor R207, sets the switch control signal V / I to a high level, turning on the switch module and enabling the linear power supply's main circuit to generate current.

[0063] When the sampling current value Isense is adjusted by the proportional link I m Reaching the set current I set After that, the seventh operational amplifier U7 in the constant current loop outputs a negative voltage (for example -12V), which turns on the second diode D202, and the constant current loop is cut in to control the switch tube module. The output voltage of the linear power supply begins to rise linearly and enters the constant current charging stage. Figure 6 shown.

[0064] During the linear rise of the output voltage of the linear power supply, the voltage feedback value output by the differential sampling link is V fb The voltage sent to the inverting input of the third op amp U3 is the superimposed voltage. , when the superimposed voltage Exceeding the set voltage V setWhen , the third operational amplifier U3 outputs a negative voltage, controlling the first diode D201 to conduct and the second diode D202 to cut off, the constant current loop is naturally cut out, and the constant voltage loop is cut in, controlling the switch tube module until the output voltage reaches the final target value.

[0065] Using the relationship of constant pressure ring: It can be seen that when the constant current loop works, the output voltage rises linearly. and VREF are fixed values, V fb0 Increase linearly. When the sum of the three terms reaches the set voltage V set When the constant voltage loop works, the output current decreases, and the rate of change of the output voltage decreases. Since VREF is a fixed value, V fb0 Continue to rise under the control of the constant pressure ring to maintain the sum of the three equal V set .

[0066] Since the conventional constant voltage loop meets the sampling voltage V fb =V fb0 = Vset It will cut in when it meets the control function, and the constant pressure ring of this embodiment meets the control function. It will immediately cut in and control the output voltage of the linear power supply. When the constant voltage loop is turned on, the constant current loop can be automatically switched to the constant voltage loop in advance compared to the traditional constant voltage loop, so as to avoid the problem of power supply output voltage overshoot.

[0067] At the same time, after the constant pressure ring is cut in, due to Gradually decreases, making V fb Gradually increase, that is, the output voltage of the linear power supply gradually increases in a smooth transition manner (such as Figure 6 The circled part in the middle gradually reaches the final target voltage Vset-VREF , and enters the constant voltage charging stage under the control of the constant voltage ring.

[0068] Considering that some loads require a smaller charging current during the constant current charging stage, for example <1mA, Since there are often dummy loads with a certain resistance on the output side of the power supply, these dummy loads will absorb part of the current output by the power supply, thereby preventing the load from being charged to the target voltage.

[0069] In order to solve the above-mentioned problems faced by low-current constant-current charging, this embodiment sets a current compensation link in the constant-current loop to compensate for the shunt generated by the remaining branches on the output side of the power supply.

[0070] Specifically, if Figure 5 As shown, this embodiment provides a fourth op amp U4 in the current compensation link. The non-inverting input of the fourth op amp U4 is connected to the negative voltage sampling point VOUT- via a voltage divider resistor R208, connected to the reference ground via a voltage divider resistor R209, and connected to the reference ground via a filter capacitor C205. The output of the fourth op amp U4 is reversely connected to its inverting input and then to the inverting input of the seventh op amp via a first compensation resistor R218.

[0071] The compensation principle is: First, the input terminal of the seventh op amp U7 is virtually shorted. Applying the superposition principle, we can get: ; Then we get: .

[0072] Where, (VOUT-)<0 , so we can know I m > I set That is, when the constant current loop is working, I m Can gradually rise and exceed I set In other words, the output current of the linear power supply can be appropriately increased to prevent the load from being unable to charge to the target voltage due to current diversion from other branches on the output side when outputting low current. By properly adjusting the parameter ratio of the first compensation resistor R216 and the second compensation resistor R218, the missing current can be accurately compensated.

[0073] Configure the resistance value of the voltage divider resistor R208 to make the current output through the current compensation link extremely small, and the current value can only be adjusted during the low current constant current charging stage. I m It has a significant impact on the current value. I m The impact can be ignored, so that the charging current of the load can be stabilized at the set current.

[0074] The analog switch control signal V / I generated by the constant voltage loop and constant current loop in conjunction with the pull-up circuit is transmitted to the switch tube module to control the conduction degree of the switch tube, so as to control the linear power supply to output constant current first and then constant voltage.

[0075] like Figure 4As shown, in this embodiment, two main power MOS tubes Q5 and Q6 are configured in the switch tube module. The two main power MOS tubes Q5 and Q6 are connected in parallel and shunted to increase the output power of the linear power supply. Therefore, the switch tube module is also a power amplifier module.

[0076] Specifically, current-limiting resistors R117 and R119 can be connected between the gate and source of the two main power MOS transistors Q5 and Q6, respectively, to limit the loop current. The drains of the two main power MOS transistors Q5 and Q6 are connected to the bus voltage output point VBUS, respectively, and the sources are connected to the voltage reference point OUT through a sampling resistor R120. The analog switch control signal V / I is transmitted to the gates of the two main power MOS transistors Q5 and Q6 through resistors R116 and R118, respectively. When the constant current loop is activated, it controls the gate-source voltage of the two main power MOS transistors Q5 and Q6 until the load current stabilizes at the set current. At this time, the bus voltage VBUS in the linear power supply charges the load. When the output voltage reaches a voltage value that is less than the target voltage by an advance amount, the constant voltage loop is activated, controlling the gate-source voltage of the two main power MOS transistors Q5 and Q6 until the load voltage reaches the target voltage and maintains the load voltage.

[0077] In the case where the load is a battery cell, some battery cells need to undergo voltage self-holding test and discharge test after being fully charged. In order to enable the linear power supply of this embodiment to meet the voltage self-holding test requirements and discharge test requirements of the battery load, this embodiment also provides a load voltage self-holding circuit and a discharge circuit on the output side of the linear power supply, such as Figure 4 As shown, to enrich the functions of linear power supply.

[0078] In some embodiments, the load voltage self-holding circuit can be formed by connecting electronic components such as a switch tube Q8 and holding resistors R123-R125. The switch tube Q8 can be an N-channel MOS tube to control the output voltage of the linear power supply.

[0079] Specifically, the drain of MOS transistor Q8 can be connected to the voltage reference point OUT, the source to the load, and the gate to the self-holding signal (control 3). Holding resistors R123-R125 are connected in series across the battery load. When the battery load requires a voltage self-holding test, the self-holding signal (control 3) is set to a low level, turning off MOS transistor Q8. This forms a loop between the load and holding resistors R123-R125, allowing the load to maintain voltage through holding resistors R123-R125. After the voltage self-holding test is complete, the self-holding signal (control 3) is set to a high level, saturating MOS transistor Q8 and ensuring normal power flow between the linear power supply and the load.

[0080] In some embodiments, the discharge circuit may be formed by connecting electronic components such as a switch element Q7 and a discharge resistor R121. The switch element Q7 may be an N-channel MOS transistor to control the on / off of the discharge path between the load and the discharge resistor R121.

[0081] Specifically, the drain of MOS transistor Q7 can be connected to the load, the source can be grounded via discharge resistor R121, and the gate can receive a discharge signal (control 2). When the load requires a discharge test, the discharge signal (control 2) is set high, turning on MOS transistor Q7 and discharging the charge in the load to ground via discharge resistor R121. After the discharge test is complete, the discharge signal (control 2) is set low, turning off MOS transistor Q7 and disconnecting discharge resistor R121, thus ensuring normal output of the linear power supply.

[0082] Compared with a traditional switching power supply, the linear power supply of this embodiment has no switching frequency ripple in the bus voltage, and the bus voltage is absolutely stable with almost no fluctuation. Therefore, using the linear power supply of this embodiment to charge the battery cell can greatly improve the effect of the battery cell insulation test.

[0083] This embodiment uses a two-stage DC bus voltage structure, which allows for easy switching between low and high voltages, extending the test range. During low-voltage testing, switching to the low-voltage bus allows for a higher current output and resolves issues such as excessive losses and excessive heating in the main power MOS transistors Q5 and Q6.

[0084] Of course, the above embodiments are intended only to illustrate the technical solutions of the present invention, and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the above embodiments, or to replace some of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed for protection by the present invention.

Claims

1. A constant voltage loop and constant current loop automatic switching circuit, used to control the power supply to charge the load with constant current first and then constant voltage; characterized in that: A voltage reference point and a negative voltage sampling point are configured on the output side of the power supply, a capacitor is connected in series between the voltage reference point and the negative voltage sampling point, and the voltage reference point is used as a reference ground for a constant voltage loop and a constant current loop; The constant pressure ring is equipped with: The differential sampling link includes a first operational amplifier, wherein the inverting input terminal of the first operational amplifier is connected to the negative voltage sampling point through a parallel branch of an input resistor and an input capacitor, the non-inverting input terminal is connected to the reference ground, and the output terminal is reversely connected to the inverting input terminal of the first operational amplifier through a parallel branch of a differential resistor and a differential capacitor; the first operational amplifier outputs the feedback value of the output voltage of the power supply V fb ,and ;in, ,and R201 is the resistance value of the input resistor, R202 is the resistance of the differential resistor, VOUT- is the voltage value at the negative voltage sampling point; k is the proportional coefficient of the differential sampling link, is the rate of change of the output voltage of the power supply; A DC bias link includes an instrument amplifier, the non-inverting input of the instrument amplifier receives the feedback value V fb , the inverting input terminal is connected to the reference ground, and the output superimposed voltage V fb + VREF ;in, VREF is the DC bias voltage of the instrumentation amplifier; The integration link is composed of an integration circuit formed by a third operational amplifier and a peripheral circuit. The inverting input terminal of the third operational amplifier receives the superimposed voltage output by the instrumentation amplifier, and the non-inverting input terminal receives the set voltage. V set , the output end is connected to the cathode of the first diode, the anode of the first diode is connected to the pull-up circuit, and an analog switch control signal is generated to control the conduction degree of the switch tube configured on the output side of the power supply; The constant current loop is configured with: The proportional link is composed of an operational amplifier and a peripheral circuit to form a proportional circuit. The inverting input terminal of the operational amplifier receives the sampled current value at the voltage reference point, the non-inverting input terminal is connected to the reference ground, and the output current value after proportional adjustment is obtained. I m ; The integration link is composed of a seventh operational amplifier and a peripheral circuit to form an integration circuit, and the inverting input terminal of the seventh operational amplifier receives the current value I m , the non-inverting input terminal receives the set current value I set The output end is connected to the cathode of the second diode, and the anode of the second diode is connected to the pull-up circuit, which is used to adjust the potential of the switch control signal.

2. The automatic switching circuit of the constant voltage loop and the constant current loop according to claim 1, characterized in that: The constant current loop also includes: The current compensation link includes a fourth operational amplifier, wherein the non-inverting input terminal of the fourth operational amplifier is connected to the negative voltage sampling point, the inverting input terminal is connected to the output terminal of the fourth operational amplifier, and the output terminal of the fourth operational amplifier is connected to the inverting input terminal of the seventh operational amplifier. By reducing the current value of the inverting input terminal of the seventh operational amplifier, the constant current loop works. I m Gradually increase and exceed I set , to compensate for the current absorbed by the dummy load on the output side of the power supply.

3. The automatic switching circuit of the constant voltage loop and the constant current loop according to claim 2, characterized in that: The output terminal of the fourth operational amplifier is connected to the inverting input terminal of the seventh operational amplifier through the first compensation resistor connected in series with the fourth operational amplifier, and the current value output by the proportional link is I m The current is transmitted to the inverting input terminal of the seventh operational amplifier through the second compensation resistor; when the target current is less than 1mA In the constant current working mode, the ratio of the first compensation resistor to the second compensation resistor is determined according to the current absorbed by the dummy load.

4. The automatic switching circuit between the constant voltage loop and the constant current loop according to claim 3, characterized in that: A resistor voltage divider network is further configured in the current compensation link. The resistor voltage divider network is connected between the negative voltage sampling point and the reference ground. The voltage divider node is connected to the non-inverting input terminal of the fourth operational amplifier. The non-inverting input terminal of the fourth operational amplifier is connected to the reference ground through a filter capacitor.

5. The automatic switching circuit of the constant voltage loop and the constant current loop according to any one of claims 1 to 4, characterized in that: The proportional link includes two stages of operational amplifiers, namely the fifth operational amplifier and the sixth operational amplifier; the inverting input terminal of the fifth operational amplifier receives the sampled current value at the voltage reference point, the non-inverting input terminal is connected to the reference ground, and the output terminal is connected to its own inverting input terminal and the inverting input terminal of the sixth operational amplifier respectively, the non-inverting input terminal of the sixth operational amplifier is connected to the reference ground, the output terminal is connected to its own inverting input terminal, and outputs the current value after the proportional adjustment I m .

6. The automatic switching circuit between the constant voltage loop and the constant current loop according to claim 5, characterized in that: A sampling resistor is connected in series at the voltage reference point, and the voltage across the sampling resistor is used as the sampling current value at the voltage reference point; the set current value I set Reflected in voltage.

7. A linear power supply comprising: A rectifier circuit, which is used to rectify the input AC power into a DC power; a current limiting and voltage stabilizing circuit, which is used to perform current limiting and voltage stabilization processing on the DC power output by the rectifier circuit, and output a stable DC bus voltage; A switch module, which is used to connect or disconnect the line between the DC bus voltage and the power output side; It is characterized in that it also includes a constant voltage ring and a constant current ring automatic switching circuit as described in any one of claims 1 to 6, and the switch control signal output by the constant voltage ring and the constant current ring automatic switching circuit controls the conduction degree of the switching tube module so that the linear power supply first charges the subsequent load with constant current and then with constant voltage.

8. The linear power supply according to claim 7, characterized in that: Two parallel MOS tubes are configured in the switch tube module, and the gate-source voltages of the two MOS tubes are adjusted using the switch control signal to adjust the conduction degree of the two MOS tubes.

9. The linear power supply according to claim 6, characterized in that: The rectifier circuit is a 7-fold voltage rectifier circuit constructed by diodes and capacitors; The current limiting and voltage stabilizing circuit comprises: A first MOS transistor, whose drain is connected to the DC output side of the rectifier circuit through an anti-reverse bias diode, and whose source is connected to its gate through a second current-limiting resistor; a second MOS transistor, wherein the drain is connected to the gate of the first MOS transistor, the source of the second MOS transistor is connected to the gate of the second MOS transistor via a third current-limiting resistor, and is connected to the DC bus voltage terminal via a charging current-limiting resistor; a third MOS transistor, a drain of which is connected to the gate of the second MOS transistor, and a source of which is connected to the gate of the third MOS transistor via a fourth current-limiting resistor; a resistor voltage divider circuit, connected between the source of the second MOS transistor and ground, with a voltage divider node connected to the gate of the third MOS transistor; The voltage regulator tube has a cathode connected to the source of the third MOS tube and an anode grounded.

10. The linear power supply according to any one of claims 7 to 9, characterized in that: Also includes: A load voltage self-holding circuit, comprising a switch connected between the voltage reference point and the load and a holding resistor connected across the load, wherein the switch is disconnected when the load requires voltage self-holding, so that the load and the holding resistor form a loop; The discharge circuit includes a switch element connected to the positive electrode of the load and a grounded discharge resistor. The switch element is turned on when the linear power supply stops outputting voltage and the load needs to be discharged, and the electrical energy in the load is released through the discharge resistor.

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